Measuring apparatus



Jan. 23, 1945.

H. S. JONES MEASURING APPARATUS Filed May 2'7, 1942 TUE HARRY S JONES ATRNEY.

Patented Jan. 23, 1945 UNITED STATES PATENT OFFICE Brown InstrumentCompany, Pa., a corporation of Pennsylvania Philadelphia,

Application May 27, 1942, Serial No. 444,747

13 Claims.

The present invention relates to improved apparatus for measuring and/orutilizing for control and analogous purposes minute direct currents suchas those resulting from the voltage variations of thermocouples orphotovoltaic cells.

An object of the invention is to provide novel and effective means forconverting a minute direct current into an alternating current which maybe readily amplified for measurement, control and other purposes.

Another object of the invention is to provide an improved arrangementfor producing alternating current from a direct current source ofelectromotive force which is characterized by the simplicity andeffectiveness of the apparatus required, and particularly by the factthat it does not include, nor require, any physically movable parts.

A further object of the invention is to effect a novel and desirablecombination of means for converting direct current into alternatingcurrent with potentiometric measuring apparatus to thereby produce anovel and relatively simple form of self balancing potentiometerinstrument which may follow the approved practices of the art in respectto many of its features.

In one embodiment of the invention I utilize the source of small directcurrent electromotive force under measurement to create a pulsatingcurrent of regular frequency by connecting the current source in circuitwith a resistive device having an appreciable temperature coefiicient ofresistance, and therefore, varying in resistance in accordance with thetemperature thereof and heating the resistance with suitable regularityand frequency by means advantageously consisting of a high frequencyoscillator from which high frequency alternating current modulated atthe desired frequency, for example 60 cycles, is impressed on theresistance. The flow of this modulated high frequency current throughthe resistive device produces variations in the conductivity of thelatter at the frequency at which the high frequency current ismodulated, and consequently, causes pulsations in the current flow inthe circuit which connects the direct current source to the resistivedevice. The pulsating current thus created is translated by suitableinductive resistance or other apparatus, such as an ordinarytransformer, into alternating current which may be amplified by the useof an electronic amplifier and utilized for the purpose of controllingthe selective actuation of relatively rugged relays or a reversibleelectrical motor. A suitable filter is also provided for preventing thehigh frequency alternating current from being impressed on the inputcircuit of the amplifier and thus affecting the operation of theamplifler and the apparatus controlled thereby.

In a preferred embodiment of the invention I employ two temperatureresponsive resistances as the resistive device for converting the smalldirect current under measurement into an alternating current of regularfrequency. In this embodiment a separate high frequency oscillator isprovided for supplying modulated high frequency current to each of theresistances. Specifically, the resistances are connected in oppositebranches of a bridge circuit on which the small direct current to bemeasured is impressed and the oscillators are so adjusted that pulses ofhigh frequency energ are impressed across the resistances duringalternate half cycles of the modulated frequency. That is to say, highfrequency energy is supplied first to one resistance for increasing itsmagnitude during one half cycle of the modulating frequency; highfrequency energy is supplied to the second resistance for increasing itsmagnitude. The pulsating direct currents which are created by thevariations in value of the resistances are converted by a transformerthe primary winding of which is connected in the bridge circuit and iscenter tapped whereby an alternating current of the same frequency asthe modulating frequency but of one phase or of opposite phase dependingupon the polarity of the impressed direct current will be derived in thesecondary winding of the transformer.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the.invention, however, its advantages and specific objects attained withits use, reference should be had to the accompanying drawing anddescriptive matter in which I have illustrated and described a preferredembodiment of the invention.

Of the drawing:

Fig. 1 is a diagrammatic representation of a preferred embodiment of myinvention; and

Fig. 2 illustrates a modification of the arrangement of Fig. 1.

Referring to Fig. 1 of the drawing there is illustrated in schematicform an electronic device, generally indicated by the referencecharacter I, for producing effects in accordance with the extent ofunbalance of a potentiometric measuring circuit 2 which controls theoperation circuit 2 is unbalanced in accordance with the variations in aquantity to be measured and because of the small magnitude of theunbalanced electromotive forces produced in the potentiometric circuitit is not practicable, nor desirable, to have the said effects produceddirectly by the potentiometric circuit.

More specifically, an arrangement is illustrated in the drawing formeasuring and recording the temperature within a furnace I in theinterior which a thermocouple 4 is arranged so as to be responsive toslight changes in the temperature within the furnace. The thermocouplel, which may be located at a distance from the remainder of thepotentiometrlc measuring circuit, has its terminals connected by a pairof conductors I and I to the terminals of the potentiometric measuringcircuit 2. The potentiometric measuring circuit 2 is preferably of thenull point type and includes a slidewire resistance I and an associatedcontact 8 which is adapted to be moved along the length of the slidewireresistance 1. The potentiometric circuit 2, illustrated schematically inthe drawing, may be of an suitable type such as the Brown potentiometricmeasuring circuit disclosed in Patent 2,150,502 issued to T. R.Harrison, E. H. Grauel and J. E.'Kessler on March 14 1939.

The movable contact 2 is mechanically connected to a suitable carrierwhich, for example, may be in the form of an internall threaded nut lwhich is adapted to ride on a screw threaded rod II which is supportedby suitable bearings l I and is rotated in one direction or the otherunder control of the thermocouple I. A reversible electrical motorgenerally designated by the reference character I2 is mechanicallycoupled in any convenient manner to the screw threaded rod II to rotatethe latter at the desired speed and in the desired direction to therebymove the contact I along the slidewire resistance I to rebalance thepotentiometric measuring circuit 2 whenever the latter is unbalanced inresponse to a change in electromotive force produced by the thermocouple4,

The contact 8 is a bridging contact connecting the point It on theslidewire resistance 1 to a corresponding point on a slidewireresistance ll which is arranged alongside the resistance 1. Theresistance I I has one end connected by the conductor to one terminal oithe thermocouple 4, and is employed for the purpose of avoidingmeasurement inaccuracies due to variations in resistance to the flow ofcurrent generated by the thermocouple l which would otherwise resultfrom variations in the relative resistances oi the portions of theresistance 1 at opposite sides of the point IS.

The other terminal of the thermocouple 4 is connected by means of theconductor 8 to the center tap on the primary winding i5 of an iron coretransformer l6 having a secondary winding 11. One end terminal of theprimary winding i5 is connected by a conductor l8 in which a lamp i9 isinserted to one terminal of the secondaiy winding of an air coretransformer 2| having primary windings 22 and 23. The other end of thetransformer primary winding is is connected by a conductor 24 in which alamp 25 is inserted to one end terminal of the secondary winding 28 ofan air core transformer 21 having primary windings 28 and 29. The otherends of the air core transformer secondary windings 2a and 28 areconnected together-by a conductor of the electronic device i. Thepotentiometric 30 as shown, and the conductor 30 is connected to theother terminal oi. the potentiometer circuit 2. A condenser 3| isconnected in shunt to the lamp i9 and secondary winding 20 and acondenser 32 is connected in shunt to the lamp 25 and secondary winding25. The purpose of condensers 3i and 32 is explained hereinafter.

The unbalanced electromotive forces which are produced in thepotentiometric network 2 upon variation in the electromotive forcedeveloped by the thermocouple l are impressed between the center tap onthe transformer primary winding i5 and the conductor 30. The arrangementconsistin of the lamps i9 and 25 and the transformer windings I5, 20 and25 comprises a parallel circuit and is utilized for the purpose ofconverting the potentiometrlc unbalanced direct currents into pulsatingcurrents which are translated by the transformer it into an alternatingcurrent of one phase or of opposite phase depending upon the polarity ofthe unbalanced direct currents derived from the potentiometer.

To this end the filaments of the lamps I! and 25 are composed of amaterial having an appreciable temperature coefficient of resistance.When resistances of such material is employed, the relationship betweenthe current flow through the the lamps l9 and 25 and the resistance ofthe filaments is non-linear. As the current through the lamps isincreased the filament temperature is raised and because of thetemperature coefiicient of resistance possessed by the filament theresistance of the lamps is correspondingly increased. The lamps l9 and25 may have nickel filaments which have a positive temperaturecoefiicient of resistance, or if desired. lamps having a negativetemperature coeiilcient of resistance such as carbon filament lamps maybe utilized instead. Resistances of the type sold by Western ElectricCo. under the trade name of Thermistors may be also employed if desired.Such resistances have a lar e negative temperature coeiilcient ofresistance, and in addition have low heat capacity. The lamps i5 and 25are preferably so constructed that the mass of the filaments issuiliciently small to permit rapid temperature and consequent resistancevariations thereof, for example, of the order of 60 cycles per second.

This property of the lamps l9 and 25 is utilized in accordance with thepresent invention for the purpose of periodically increasing anddecreasing the resistance of the circuit path through which theunbalanced potentiometric direct currents flow and thereby for creatinga pulsating direct current flow through the transformer primary windingi5 which is converted by the transformer I8 into an alternating currentof one phase or of opposite phase depending upon the direction of thedirect current flow from the potentiometric circuit 2 through thetransformer primary winding l5.

Such alternate increase and decrease in the resistance of the lamps i9and 25 is eil'ected by impressing on each lamp a high frequencyalternating current modulated at a suitable frequency. for example, 60cycles per second and derived from associated transformer secondarywindings 20 and 26. As is explained hereinafter, the envelope of themodulated high frequency current derived from the transformer secondarywinding 20 is preferably displaced with respect to the modulated highfrequency current derived from the transformer secondary winding 26. Anelectronic oscillator 83 is provided for inducing the The oscillator 33includes an electronic valve 35 having an anode, a control electrode, acathode and a heater filament which is electrically connected in asuitable manner so as to normally oscillate at the desired highfrequency. The oscil;

latory condition of the electronic valve 35 is pro moted by anelectrical interlinkage between the control electrode or input circuitand the anode or output circuit. As shown, this interlinkage is aninductive one and is obtained by means of the two inductively associatedwindings Or coils 22 and 23 which are connected respectively in theinput and output circuits of the valve 35.

The oscillator 34 includes an electronic valve 36 having an anode, acontrol electrode, a cathode and a heater filament and which also isconnected so as to normally oscillate at the desired frequency. Theoscillatory condition of the valve 36 is promoted by an electricalinterlinkage between the transformer primary winding 28 which is con--nested in the input circuit of the valve 36 and the primary winding 29which is connected in the output circuit of valve 26. The electronicvalves 35 and 36, if desired may be contained within a single envelopeas illustrated in the drawing. Energizing current is supplied the heaterfilaments of the electronic valves 35 and 36 from the secondary winding31 of an iron core transformer 38 having a line voltage primary winding39 and a high voltage secondary winding 40. The filaments of theelectronic valves 35 and 36 are connested in parallel and the parallelconnection is connected by conductors (not shown) to the ter mlnals ofthe transformer secondary winding 31.

Energizing voltage is supplied to the output circuits of the electronicvalves 35 and 36 from the transformer secondary winding 40. The outputcircuit of valve 35 may be traced from the upper terminal of thetransformer winding 46 as seen in the drawing through a conductor 4 I,in which the transformer primary winding 23 is connected, to the anodeof valve 35 and from the cathode thereof to a center tap 43 on thewinding 40. The output circuit of the valve 36 may be traced from thelower terminal of the secondary winding 40 through a conductor 42 inwhich the transformer primary winding 29 is connected to the anode ofvalve 36 and from the cathode of the latter to the center tap on thewinding 40.

The input circuit of the valve 35 may be traced from a .po nt 44 on thetransformer secondary winding 40, through a conductor 45 in which thewinding 22 is inserted to the control electrode of the valve 35 and fromthe cathode of the valve 35 to the center tap 43. The point 44 on thetransformer secondary winding is somewhat negative with respect to thepotential of the center tap 43 during the half cycle of the alternatingcurrent supply when the upper terminal of the winding 40 s positive. Theinput circuit of the valve 36 may be traced from a point 46 on thewinding 40, which is somewhat negative with respect to the potential ofthe center tap 43 during the half cycle when the lower terminal of theWinding 40 i positive, to a conductor 41 in which the winding 28 isCOD-,- nected to the control electrode of valve 36.

By energizing the output circuits of the electronic valves 35 and 36from the center tapped transformer secondarywinding 40, high frequencyenergy is impressed on the lamp l9 during one half cycle of thealternating current supply which increases in magnitude while the highfrequency energy impressed on the lamp 25 decreases in magnitude, andduring the next half cycle of the alternating current supply highfrequency energy is impressed on the lamp 25 which increases inmagnitude while the high frequency energy impressed on the lamp l9decreases in magnitude. That is to say, the envelope of the modulatedhigh frequency current derived from the transformer secondary winding 20is displaced approximately with respect to the envelope of the modulatedhigh frequency current derived from the transformer secondary winding26. Thus, high frequency energizing currents are alternately impressedon the lamps l9 and 25 at the frequency of the alternating currentsupply source.

In accordance with the present invention the alternating current supplyfor the transformer primary winding 39 is preferably of commercialfrequency, for example, 60 cycles and may be derived from alternatingcurrent supply lines L and L When 60 cycle alternating current isimpressed on the transformer primary winding 39, high frequency energymodulated at 60 cycles per second is alternately impressed on the lampsl9 and 25. Condensers 48 and 49 are connected in parallel to thetransformer primary winding 23 and 29 respectively for tuning the latteras required to produce the necessary feedback of energy to the inputcircuits of the electronic valves 35 and 36 to establish the desiredhigh frequency oscillations. Condensers 3| and 32 reviously referred toare used to by-pass high frequency current and thereby prevent it frompassing through the primary winding l5 of the transformer l6 and throughthe thermocouple and measuring circuits. Therefore, substantially all ofthe high frequency energymust dissipate itself in the temperatureresponsive resistances or lamps l9 and 25.

Modulated high frequency current is particularly adapted for the purposeof producing Variations in resistance of the lamps l9 and 25 at thedesired frequency since no interference with the potentiometricmeasuring circuit or the alternating current supp-1y source employed foroperating the reversible electrical motor l2 results. The frequency ofthe high frequency source may be of the order of normal radiofrequencies, if desired, or may be a comparatively high frequency suchas 0.5 to 10 megacycles. The latter order of frequencies is preferablefrom the standpoint of simplicity and economy since the condensers 3|,32, 48 and 49 and the transformers 2| and 21 can then be very small andinexpensive.

With the arrangement described, the flow and direction of flow ofcurrent through the circuit from the point 50 0f the potentiometricmeasuring circuit 2 through the variable lamp resistances l9 and 25. thetransformer primary winding l5, and the brid ing contact 8 to the pointl3 of the potentiometric measuring circuit 2 depends upon the relationbetween the electromotive force produced by the thermocouple 4 and thepotential difference between the potentiometric circuit points l3 and50. The thermocouple 4 is so connecteci to the potentiometric measuringcircuit that the electromotive force of the thermocouple opposes thepotential difference between the points l3 and 50. The potentialdifference between the points l3 and 50 is increased and decreased bymovement of the contact 8 to the right and to the left, respectively.With suitable adjustments of the contact 8, the potential differencebetween the points l3 and 50 will be equal and opposite to theelectromotive force produced by the thermocouple 4 and no current willflow through the circuit branch including the lamps l9 and 25. On anincrease in the thermocouple electromotive force above the potentialdifference between the points i3 and 50, current will flow in onedirection through the circuit branch including the lamps l9 and 25 andthrough the transformer primary winding l5 and such current fiow maythen be eliminated by a suitable adiustment oi the bridging contact 8 tothe right. Conversely, when the electromotive force of the thermocouple4 falls below the potential difference between the potentiometriccircuit points i3 and 50, the resultant current flow through the lampsl8 and and the transformer primary winding l5 will be in such adirection as to be eliminated by a suitable adjustment of the contact 8to the left.

As is illustrated more or less diagrammatically in the drawing, thecontact 8 is adjusted along the slidewire resistance 1 by the operationof the reversible electrical motor |2 which is shown as having its rotor5| mechanically coupled to the threaded shaft Ill. The reversibleelectrical motor l2 has a pair of terminals 52 and 53 which areconnected to the output circuit of the electronic device I, and also hasa pair of terminals 54 and 55 which are connected through a condenser 56of suitable value to the alternating current supply conductors L and L.

For its intended use the motor i2 may be of the form schematically shownin the drawing and comprising a rotor 5| and two pairs of oppositelydisposed field poles (not shown), on one pair of which a winding 51 iswound and on the other pair of which a winding 58 is wound. Winding 51has its terminals connected to the motor terminals 54 and 55 and issupplied with energizing current from the alternating current supplyconductors L and L through the condenser 56. Due to the action of thecondenser 55 the current which flows through the motor winding 51 willlead the voltage of the alternating ply lines L and L by approximately90.

The current supplied to the winding 58 of the motor |2 by the electronicdevice I is approximately in phase with or displaced 180 with respect tothe voltage of the alternating current supply lines L and L andestablishes a field in the rotor 5| which is displaced approximately 90in one direction or the other with respect to that established thereinby the winding 51. Reaction between the field set up by the winding 58with that set up by the winding 5! establishes a rotating field in therotor 5| which rotates in one direction or the other depending uponwhether the winding 58 is energized with current in phase with thevoltage of the alternating current supply lines L and L or displaced 180with, as is explained in detail hereinafter.

The direction and duration of rotation of the motor I2 is controlled inaccordance with the direction and extent of unbalance of thepotentiometric measuring circuit 2 so that upon rotation of the motor |2the contact 8 is adjusted in the proper direction to rebalance thepotentiometric measuring circuit 2. If desired, a pen 59 may be mountedon the carriage 9 which carries the contact 8 and may be arranged incooperative relation with a recorder chart 50 to thereby provide acontinuous record oi the temperature to which the thermocouple 4 issubjected. The

current sup in phase therechart 60 may be a strip chart as shown and isadapted to be driven in any convenient manner as, for example, by aunidirectional electrical motor 6| through suitable gearing (not shown)so that a record of the temperature to which the thermocouple 4 issubjected will be recorded as a continuous line on the chart 60.

Fundamentally, the circuit through which the unbalanced potentiometercurrents flow and in which the lamps l9 and 25 and the transformerprimary winding l5 are connected is a polarized switching mechanism, theoscillators 33 and I4 cooperating to periodically and alternately varythe resistance of the filaments of lamps l9 and 25. For purposes ofillustration it may be assumed that the resistance of the filament oflamp I9 is increased during the first half cycle of the alternatingvoltage supplied by the supply conductors L and U, for example, when theupper terminal of the transformer secondary winding 4|] is positive withrespect to the lower terminal thereof, and that the resistance of thefilament of the lamp 25 is increased during the second half cycle whenthe upper terminal of the winding 40 is negative with respect to thelower terminal thereof. I

When the potentiometric measuring circuit 2 is balanced, no currentflows in the circuit branch between the potentiometric circuit points I!and 50. When the temperature to which the thermocouple 4 is subjectedincreases, the unbalanced direct current in the potentiometric circuitflows in the direction from the potentiometric circuit point l3 throughthe conductor 5, thermocouple 4, conductor 6, through the oppositehalves of the transformer primary winding |5, in circuit with one halfof which the lamp I9 is connected and in circuit with the other half ofwhich the lamp 25 is connected, and through the conductor 62 to thepotentiometer circuit point 50. Conversely, when the temperature towhich the thermocouple 4 is subjected decreases, the unbalanced directcurrent in the potentiometric circuit flows in the opposite directionthrough the circuit path just traced, namely, from the potentiometriccircuit point 50 to the potentiometric circuit point i2.

When the temperature to which the thermocouple 4 is subjected increases,the resistance of the filament of lamp i9 is "increased relatively tothe resistance of lamp 25 during the first half cycle of the alternatingvoltage supplied to the transformer primary winding 39 whereupon thegreater part of the unbalanced potentiometer direct current flows fromthe potentiometer circuit point l3 to conductor 5, thermocouple 4,conductor 6, the lower half of transformer primary winding l5 throughconductor 24, lamp 25, transformer secondary winding 25 and conductor 82to the bridge point 50. Part of the unbalanced potentiometer directcurrent will flow through the upper half of the transformer primarywinding 5 to the lamp IS, the transformer secondary winding 20, theconductor 52 and the bridge point 50, but a predominant part of thecurrent will flow through the lower half of the winding l5 becauseduring this half cycle the resistance of the lamp 25 is considerablyless than the resistance of the lamp IS. The excess in the current flowthrough the lower half of the transformer primary winding l5 over thecurrent flow through the upper half of the transformer primary windingoperates to induce a voltage in the transformer secondary winding I!which is of the proper polarity to cause the upper terminal of thelatter winding to become positive with respect to the lower terminal.

During the second half cycle of the alternating voltage supply to thetransformer primary winding 39, the resistance of the filament of thelamp 25 will be increased to a value greater than the value ofresistance I9, this efiect being partially accomplished by resistance ofthe filament of lamp I9 decreasing from the value assumed during thefirsthalf cycle. Accordingly, during the second half cycle of thealternating current supply, the predominant part of the unbalancedpotentiometer direct currents will flow from the potentiometer bridgepoint I3 through the upper half of the transformer primary winding I5and through the lamp I9 to the potentiometer circuit point 50. Part ofthe unbalanced potentiometer direct currents will tend to fiow throughthe lower half of the transformer primary winding I5 and through thelamp 25 during the second half cycle but the predominant part of theunbalanced potentiometer direct currents will fiow through the upperhalf of the transformer primary winding I5. The excess of current fiowin the upper half of transformer primary winding I5 over that of thelower half of the winding causes the induction of a voltage in thetransformer secondary winding of the proper polarity to make the upperfiows through this circuit because during this half cycle the resistanceof the filament of lamp I9 is less than the resistance of the filamentof lamp 25. The excess in the fiow of current through the upper half ofthe transformer primary winding l5 over that through the lower half ofthe latter operates to induce a voltage in the transformer secondarywinding I I of the proper polarity to cause the potential of the upperterminal of the transformer secondary winding II negative with respectto the potential of the lower terminal. Therefore, .it will be seen thatupon an increase in the temperature to which the thermocouple 4 issubjected, an alternating voltage is produced across the transformersecondary winding H which is in phasewith the alternating voltageproduced across the transformer wecondary winding 40 and also is of thesame frequency as the alternating voltage produced across the latterwinding.

Upon a decrease in the temperature to which the thermocouple 4 issubjected, the unbalanced potentiometric direct currents fiow from thecir- Quit point 50 to the point I3. During the first half cycle of thealternating current supplied the transformer primary winding 39, thegreater part of the unbalanced direct current will flow from the circuitpoint 50 through the conductor 62,

transformer secondary winding 26, the filament of lamp 25, conductor 24,the lower half of the transformer primary winding I5, conductor 6,thermocouple 4, and conductor 5 to the potentiometric circuit point I3.The greater part of the unbalanced potentiometer direct current fiowsthrough this circuit because during this halfcycle the resistance of thefilament of lamp I9 is greater than the resistance of the filament ofthe lamp 25. The excess of current flow through the lower half oftransformer primary winding I5 over that through the upper half of thelatter causes the induction of a voltage in the transformer secondarywinding ll of the proper polarity to cause the upper terminal of thewind mg I I to become negative with respect to the potential of thelower terminal.

During the second half cycle of the alternating current supplied thetransformer primary winding 39, a. predominant part of the unbalancedpotentiometer direct current fiows from the potentiometer circuit pointthrough conductor 82, transformer secondary winding 20, the filament oflamp I9, conductor I8, the upper half of transformer primary winding I5,conductor 6, thermocouple 4 and conductor 5 to the potentiometer circuitpoint I3. The greater part of the unbalanced potentiometer directcurrent terminal to become positive with respect to the potential of thelower terminal. Accordingly, when the temperature to which thethermocouple 4 is subjected decreases, an alternating voltage of theopposite phase is induced in the transformer secondary winding I'I.

Summarizingwhen the potentiometric measuring circuit 2 is balanced,there is no current flow through the transformer primary winding I5, andtherefore, no voltage is induced in the transformer secondary windingII. Upon an increase in the temperature to which the thermocouple 4 issubjected, the pulsations in the fiow of potentiometric unbalancedcurrent produced through the transformer primary winding I5 by thevariations in resistance of the-lamps I9 and 25 operates to causetheinduction of an alternating voltage in the transformer secondarywinding I! which is in phase with the alternating voltage supplied tothe transformer primary winding 39. Conversely, upon a decrease in thetemperature to which the thermocouple 4 is subjected the pulsations inthe potentiometer unbalanced direct current through the transformerprimary winding I5 causes the induction of an alternating voltage in thetransformer secondary winding II which is approximately out of phasewith the alternating voltage supplied to the transformer primary winding39.

In the preferred embodiment of the present invention the alternatingvoltage derived in the transformer secondary winding I1 is amplified bythe electronic device I and the amplified quantity is utilized for thepurpose of energizing the phase winding 58 of motor I2 for controllingthe selective actuation of the latter for rotation in one direction orthe other. The electronic device I includes an electronic tube 63 to theinput circuit of which the alternating voltage induced in thetransformer secondary winding I1 is applied. The electronic tube 63includes two heater type triodes, which have been designated by thereference numerals 64 and 65, within the same envelope. The triode 64includes anode, control electrode, cathode, and filament elements, andthe triode 65 also includes like elements. Thefilaments of the triodes64 and 65 are connected in parallel and receive energizing current fromthe low voltage secondary winding 66 of a transformer 61 having a linevoltage primary winding 68 and high voltage secondary windings 69 and10. The conductorsto the heater filaments of the electronic tube 63 havenot been shown in order not to confuse the drawing. The primary winding68 of the transformer 61 is connected to and receives energizing currentfrom the alternating current supply conductors L and L which also supplyenergizing current to the primary winding 38 of the transformer 38. Thetransformer secondary winding 66 is also connected by means ofconductors (not shown) to the heater filaments of electronic tubes IIand I2. The heater filaments of the electronic tubes II and I2 may allbe connected in parallel with the heater filaments of the electronictube 63.

The electronic tube II includes two heater type triodes, designated bythe reference characters I9 and II within the same envelope. Both of thetriodes include anode, control electrode, cathode, and heater filaments.The electronic tube II also includes two heater type triodes, which havebeen designated by the reference numerals II and I9, within thesame'envelope. The triodes 19 and 19 each include anode, controlelectrode, cathode, and heater filament elements.

.The triode I4 of the electronic valve II is utilized as a half waverectifier to provide a source of direct current voltage for energizingthe anode or output circuits of the triodes 94, 89 and II. As shown, thecontrol electrode and cathode of the triode 14 are directly connected toeach other and the output circuit thereof isenergized by the transformersecondary winding 99 through a circuit which may be traced from the leftend terminal of the winding 99, as seen in the drawing, through aconductor TI to the anode of triode ll, the cathode thereof, and througha conductor I9 to the positive terminal of a filter generally designatedby the reference numeral 19. The negative terminal of the filter isconnected by a conductor 99 to the right end terminal of the winding 99.

The filter I9 includes a condenser 9| which operates to smooth out theripple in the output voltage of the filter between the points 92 and 99.The filter I9 also includes a resistance 94 and a condenser 99 whichoperate to smooth out the output voltage of the filter between thepoints 99 and 99. The filter I9 includes a further resistance 91 and acondenser 99 for smoothing out the output voltage of the filter betweenthe points 99 and 99. The filter, therefore, comprises three stages.Such a three-stage filter is provided because for the most satisfactoryand efficient operation it is desirable that the anode voltage suppliedto the triode 64 be substantially free from ripple whereas it is notnecessary to supply anode voltage so completely free from ripple to theoutput circuit of the triode 99. Likewise it is not necessary to supplyanode voltage as free from ripple to the triode I3 as it is to thetriode 99.

The anode circuit of the triode 99 may be traced from the filter point99, which comprises the positive terminal of the direct current voltagesupply, through a fixed resistance 99 to the anode of triode 94, to thecathode thereof, and through a cathode biasing resistance 9| which isshunted by a condenser 92 to the negative filter point 93 through aconductor 99. The cathode biasing resistance 9I and the parallelconnected condenser 92 are provided for biasing the control electrode oftriode 94 negatively with respect to the cathode.

The input circuit of the triode 9| may be traced from the cathodethrough the parallel connected resistance 9I and condenser 92 throughthe transformer secondary winding I1 and a conductor 99 to the controlelectrode of the triode H.

The output circuit of the triode 99 is resistance capacity coupled tothe input circuit of the triode 95 by means of a condenser 95 and afixed resistance 99. Particularly, the anode of the triode 94 isconnected by condenser 95 to the control electrode of the triode Blandthe control electrode of the triode 99 is connected through theresistance 98 to the conductor 93 and thereby to the cathode of thetriode 65.

The anode circuit of the triode 85 may be traced from the positiveterminal 99 of the filter 19 through a fixed resistance 91 to the anodeof asevgses the triode 99, the cathode thereof, and conductor 99 to thenegative terminal 99 of the filter.

The output circuit of the triode is resistance capacity coupled to theinput circuit of the triode II by means of a condenser 99 which isconnected between the anode of the triode 99 and the control electrodeof the triode II, and by means of a resistance 99 which is connectedbetween the control electrode of the triode II and the cathode thereof.It is noted the resistances 96 and 99 which are connected in the inputcircuits of the triodes 95 and II, respectively, operate to maintain thecontrol electrodes of the triodes 99 and 19 at the same potential astheir associated cathodes when no voltage is induced in the transformersecondary winding I1, and upon the induction of an alternating voltagein the winding I'I, resistances 99 and 99 permit the flow of gridcurrent between the control electrodes of the triodes 65 and II andtheir associated cathodes and thereby limit the extent to which thecontrol electrodes of the triodes may go positive with respect to theirassociated cathodes.

The anode circuit of the triode Il may be traced from the positive point92 of the filter 19 through a fixed resistance I99 to the anode of thetriode, to the cathode thereof, and conductor 93 to the negativeterminal 93 of the filter.

The output circuit of the triode II is resistance capacity coupled bymeans of a condenser III and a resistance I92 to the input circuits ofthe triodes I9 and I9. As illustrated, a contact III in adjustableengagement with the resistance I9! is provided for varying the point ofconnection of the control electrodes of the valves I9 and 19 to theresistance I92. The resistance I92 and contact I93 perform a dualfunction, namely, to limit the extent to which the control electrodes ofthe triodes l5 and 18 may be driven positive with respect to theirassociated cathodes, and also to vary the proportion of the signalimpressed upon the control electrodes IS and I9 from the output circuitof the triode I3. It will be noted that the signal voltage from theoutput circuit of the triode 13 is impressed simultaneously and equallyon the control electrodes of the triodes I5 and I6,

Anode voltage is supplied the output circuits of the triodes l5 and 16from the high voltage secondary winding I9 of the transformer 91. Theanode of the triode I5 is connected to the left end terminal of thetransformer secondary winding "and the anode of the triode IE isconnected to the right end terminal of the transformer secondary windingI9. The cathodes of the triodes I5 and I6 are connected together andthrough a fixed resistance I94 and a conductor I95 to the terminal 53 ofthe motor I2. The terminal 52 of the motor I2 is connected by aconductor I96 to a center tap on the transformer secondary winding I9.Thus, the triodes I5 and 16 are utilized for supplying energizingcurrent to the phase winding 59 of motor I2.

The electrical circuit shown in the drawing and described herein, forselectively controlling the operation of the reversible electrical motorI2 for rotation in one direction or the other is disclosed and is beingclaimed in application Serial No. 421,173, filed by W. P. Wills forMeasuring apparatus on December 1, 1941. Therefore, for the presentpurposes it is believed sufflcient to note that the motor I2 ispreferably so constructed that the impedance of the winding 59 is of theproper value to match the impedtain the most eflicient operation.Preferably, the

motor is so constructed that it has a high ratio of inductance toresistance, for example, of the order of 6-1 or from 8-1 at thefrequency of the energizing current supplied to it. This provides formaximum power during the running condition of the motor with the leastamount of heating, and also provides a low impedance path for brakingpurposes.

As noted hereinbefore energizing current is supplied to the motorwinding 51 from the alternating current supply conductors L and Lthrough the condenser 56. The condenser 56 is so selected with respectto the inductance of the motor winding 51 as to provide a seriesresonant circuit having a unity power factor. By virtue of the seriesresonant circuit the total impedance of the motor winding 51 issubstantially equal to the resistance of the winding, and since thisresistance is relatively low, a large current flow through the winding51 is made possible. This permits the attainment of maximum power andtorque from the motor l2. In addition, the current flow through themotor winding 51 is in phase with the voltage of the alternating currentsupply conductors L and L because of the series resonant circuit. Thevoltage across the motor winding 51, however, leads the current bysubstantially 90 because of the inductance of the winding 51,

Energizing current is supplied the motor winding 58 from the transformersecondary winding 18 through the anode circuits of the triodes 15 and 16through the circuits previously traced. A condenser I8! is connected inparallel with the motor Winding 58 and is so chosen as to provide aparallel resonant circuit having a unity power factor. This parallelresonant circuit presents a relatively high external impedance and arelatively low local circuit impedance. The relatively high externalimpedance is approximately the same as the impedance of the anodecircuits of the triodes 15 and i6 and accordingly provides efiicientoperation. The relatively low or internal circuit impedance approximatesthe actual resistance of the winding 58, and since this resistance isrelatively low, the impedance of the local circuit is also relativelylow.

During the first half cycle of the alternating voltage produced acrossthe terminals of the transformer secondary winding 18, the anode of thetriode 15 is rendered positive with respect to the center tap on thewinding 18, and during the second half cycle, the anode of the triode i6is rendered positive with respect to that center tap. Accordingly, thetriodes I and 16 are arranged to conduct on alternate half cycles of thealternating current supplied by the supply lines L and L For thecondition when the potentiometric measuring circuit 2 is balanced, novoltage is induced in the transformer secondary winding l1, andtherefore, the potentials of the control electrodes of the triodes B4and 65 and 13 remain substantially constant, and consequently, no signalis impressed upon the control electrodes of the triodes I5 and 16. Underthis condition of operation, a pulse of unidirectional current flowsfrom the anode of the triode to the cathode thereof and through themotor winding 58 during the first half cycle of the alternating voltagesupply. During the second half cycle a pulse of current flows from theanode of the triode 15 to the cathode and thence through the motorwinding 58. Since the control electrodes of the triodes 15 and 16 areconnected together, and since the potentials of these control electrodesremain substantially constant when the potentiometric measuring circuit2 is balanced, pulses of equal magnitude flow in the anode circuits ofthe triodes 15 and 16 during each succeeding half cycle of thealternating voltage supplied by the transformer secondary winding 18.

From the foregoing it will be noted that when the potentiometricmeasuring circuit 2 is balanced, pulsating unidirectional current oftwice the frequency of the alternating voltage supplied by conductors Land L is impressed on the motor winding 58. When thus energized themotor I2 is not urged to rotation in either direction and remainsstationary. Due to the relatively high direct current component of thecurrent then flowing through the motor winding 58, the core structure ofthe motor l2 tends to become saturated whereby the inductive reactanceof the motor winding 58 is relatively small, The condenser I81 in shuntto the motor winding 58 is so chosen that the condenser and motorwinding then forms a parallel resonant circuit. This saturation of thecore structure of the motor l2 operates to exert an appreciable dampingeifect on the rotor 5|, or in other words, an effect tending to preventrotation of the rotor 5|. Consequently, if the rotor 5| has beenrotating, saturation of the motor core structure operates to quicklystop the rotation.

' lines L and L Upon unbalance of the potentiometric measuring circuit2, the magnitude of the pulses of ourrent flowing in the anode circuitof one triode I5 or 16 will be increased while the magnitude of thepulses of current flowing in the anode circuit of the other triode willbe decreased. Accordingly, the pulses of unidirectional current suppliedto the motor winding 58 during the first half cycle will predominateover those supplied the motor winding 58 during the second half cycle.Such energization of the motor winding 58 operates to introduce thereinan alternating component of current of the same frequency as thatsupplied by the alternating current supply This alternating component ofcurrent will be either in phase with or out of phase with thealternating current flowing through the motor winding 51 depending uponthe direction of potentiometric unbalance and produces an alternatingmagnetic field in the motor core structure which reacts with thealternating magnetic field established by the motor winding '51 toproduce a rotating field in the m0- tor. This rotating field rotates inone direction or the other depending upon the direction ofpotentiometric unbalance and effects actuation of the motor rotor 5| forrotation in a corresponding direction. In addition, when the motorwinding 58 is so energized, the direct current component of the currentflowing therein is decreased and consequently the saturation of themotor core structure is decreased with the result that the rotor dampingeffect is reduced.

In order to permit rapid operation of the reversible electrical motor |2in effecting rebalance of the potentiometric network 2 withoutovershooting and consequent hunting occurring, the response of the motorI2 must be correlated with the unbalancing and rebalancing operations ofthe potentiometric network. This may be accomplished'by adjusting thecontact I83 along the resistance |82 which is employed for the purposeof coupling the output circuit of triode I83 to the input circuits ofthe triodes and II. The contact III! and resistance I02 may be termed asensitivity adjustment. By moving the contact Ill in an upward directionthe amplitude of swing of the control electrodes of the triodes 18 andi6 is increased for any given signal impressed on the input circuit ofthe electronic amplifier I and by moving the contact III! in a downwarddirection the amplitude of swing is decreased. This accordingly adjuststhe sensitivity of the electronic amplifier I whereby the re-- sponse ofthe reversible electrical motor I2 may be exactly correlated with theoperation of the potentiometric network.

As will be understood by those skilled in the art one or the other ofthe lamps I9 and and its associated equipment for impressing a modulatedhigh frequency electric current therein may be dispensed with if desiredand the other lamp and its associated equipment may be utilized alonefor the purpose of effecting a pulsating current flow through theprimary winding of transformer It in converting the unbalancedpotentiometric direct currents into an alternating current which may bereadily amplified and utilized for the purpose of controlling theselective actuation of the reversible electrical motor I2. When one lampI9 or 25 is dispensed with the primary winding I! of the transformer I8need not be center tapped. Such a modification is illustrated in Fig. 2of the drawing wherein the primary winding of the transformer It hasbeen designated by the reference character IS.

The use of the arrangement disclosed in Fig. 1 and utilizing two lampsII and 25 for the purpose of converting the unbalanced potentiometricdirect currents into an alternating current of one phase or of oppositephase depending upon the direction of potentiometric unbalance is to bedesired over the simplified arrangement shown in Fig. 2 because with thearrangement-of Fig. 1 any stray alternating current of the samefrequency as that supplied by the conductors L and L which is induced inthe thermocouple leads or in the potentiometric circuit is converted bythe arrangement including lamps l9 and 25 into an alternating current oftwice the frequency of the alternating current supplied by the supplylines L and L. For example, when the alternating current supplied by thelines L and U is 60 cycle current, any stray alternating currents whichmay be induced in the thermocouple or potentiometric circuit isconverted into 120 cycle alternating current. This 120 cycle alternatingcurrent has no effect upon the operation of the reversible electricalmotor I2 because of the par ticular construction of the electronicamplifier I and the connection of the reversible electrical motor I! tothe output circuit of the amplifier. The reason why 120 cyclealternating current does not affect the operation of the electronicamplifier I and the reversible electrical motor I2 is pointed out indetail in the Wills application, Serial No. 421,173 referred tohereinbefore and therefore need not be explained in detail herein.

It will be apparent that the reversible electrical motor I2 may beemployed to operate a valve I08 positioned in a fuel supply pipe I09 forvarying the supply of heating agent to the furnace 3, to the temperatureof which the thermocouple 4 is responsive, or preferably a separatereversible electrical motor may be so employed. For example, asdisclosed in the drawing, a reversible electrical motor III having twoopposed field windings (not shown) may be utilized for this mensespurpose. The reversible motor H0 is mechanically connected in anysuitable manner to the valve III! and is adapted to adjust the latter toits opened and closed positions depending upon the direction to whichthe motor I III is energized for rotation. The mechanical connection ofthe motor III to the valve III! is such as to increase and to decreasethe supply of heating agent to the furnace 3 as the temperature of thelatter falls below or rises above a predetermined level.

The motor H0 is energized for rotation in one direction or the otherdepending upon which of the two opposed field windings is energized bymeans of a switch III. The switch III includes a contact ,I I2 which iscarried by the carriage I and is disposed in operative relation with apair of elongated contact segments H3 and I I4. The contact segments IIIand Ill are insulated from each other and from the contact H2 and aredisposed end to end along the slidewire resistance 1 of thepotentiomctric measuring circuit. The adjacent ends of the contactsegments Ill and I are separated by a suitable distance and are sorelated to the slidewire resistance 1 that, when the contact III isintermediate the segments III and Ill and out of engagement withboth,the temperature within the furnace 3 will be at the desired controlpoint. The switch contact III is insulated from the slidewire resistance1 and also from the carriage 9.

The switch contact II: is connected to the alternating current supplyconductor L and the common terminal of the opposed windings of motor H0is connected to the supply conductor L. The contact segment II: isconnected by a conductor III to the other terminal of one of the opposedmotor field windings, and the contact segment III is connected byconductor ill to the other terminal of the other motor field winding.Thus, upon engagement of the contact III with the contact segment III,one of the windings of motor III] is energized and actuates the motorfor rotation in one direction, and upon engagement of the contact II2with the contact sesment I I4, the other of the windings of motor I IIis energized and actuates the motor for rotation in the oppositedirection.

Although not shown the contact segments III and Ill of the switch iIIare desirably made adjustable so that both the control point setting andsensitivity of the apparatus may be set in a manner well known in theart.

While in accordance with the provisions of the statutes, I haveillustrated and described the best form of my invention now known to me,it will be apparent to those skilled in the art that changes may be madein the form of the apparatus disclosed without departing from the spiritof my invention as set forth in the ap-- pended claims, and that certainfeatures of my invention may sometimes be used to advantage without acorresponding use of other features.

Having now described my invention what 1 claim as new and desire tosecure by letters Patent is:

1. In measuring apparatus, the combination of an adjustablepotentiometer device, means to produce unbalanced currents in saidpotentiometer device, means for converting the unbalanced potentiometercurrents into varying current of predetermined frequency, said lastmentioned means including an electrical resistive device having anappreciable temperature coefficient of resistance through which theunbalanced portion of the potentiometer current is passed, a source ofhigh the other branch of said parallel circuit to cause frequencyelectric current modulated at said predetermined frequency, and meansfor impressing said high frequency current on said resistive deviceindependently of said potentiometer to vary the temperature of saidresistive device at said predetermined frequency, means for amplifyingsaid converted currents, a reversible rotatable motor for adjusting saidpotentiometer device to reduce said unbalanced potentiometer currents,and motor control means controlled by said amplified currents to controlthe rotation of said reversible motor.

2. In measuring apparatus, the combination of an adjustablepotentiometer device, means to produce unbalanced currents in saidpotentiometer device, means for converting the unbalanced potentiometercurrent into varying current of predetermined frequency, said lastmentioned means including an electrical resistive device having anappreciable temperature coefficient of resistance through which theunbalanced portion of the potentiometer current is passed, a source ofhigh frequency electric current modulated at said predeterminedfrequency, and means for impressing said high frequency current on saidresistive device independently of said potentiometer to vary thetemperature of said resistive device at said predetermined frequency,means for amplifying said converted currents, and means actuated by saidamplified currents for adjusting said device to reduce said unbalancedpotentiometer currents.

3. The combination with a circuit including a resistive device having anappreciable temperature coefflcient of resistance, of means forimpressing a small unidirectional electromotive force on said circuit,an oscillator for producing a high frequency electrical currentmodulated at a predetermined frequency, means for impressing said highfrequency current on said device to vary the temperature of said deviceat said predetermined frequency and thereby to vary the resistance ofsaid device at said predetermined frequency, alternating current supplymeans for energizing said oscillator, and inductive control meansjointly energized by currents directly supplied by said supply means andby current flow in said circuit.

4. The combination with a parallel circuit each branch of which includesa resistive device having an appreciable temperature coefiicient ofresistance and one half of a center tapped primary winding of atransformer also having a secondary winding of means for impressing asmall unidirectional electromotive force on said parallel circuit, anoscillator for producing a high frequency electrical current modulatedat a predetermined frequency, a second oscillator for producing a secondhigh frequency electrical current modulated at said predeterminedfrequency but the envelope of which is displaced approximately 180relatively to the envelope of said first mentioned high frequencycurrent, and means for impressing said first mentioned high frequencycurrent on one branch of said parallel circuit to vary the temperatureand thereby the resistance of the. device connected therein at saidpredetermined frequency and for impressing said second mentioned highfrequency current on the other branch of said parallel circuit to varythe temperature and thereby the resistance of the device connectedtherein at said predetermined frequency whereby said unidirectionalelectromotive force alternately creates a pulsating current flow firstin one branch and then the induction of an alternating electromotiveforce in the secondary winding of said transformer of one phase or ofopposite phase depending upon the polarity of said unidirectionalelectromotive force.

5. The combination with a parallel circuit each branch of which includesa resistive device having an appreciable temperature coefficient ofresistance and one half of a center tapped primary winding of atransformer also having a secondary winding of means for impressing a.small unidirectional electromotive force on said parallel circuit, anoscillator for producing a high frequency electrical current modulatedat a predetermined frequency, a second oscillator for producing a secondhigh frequency electrical current modulated at said predeterminedfrequency but the envelope of which is displaced approximatelyrelatively to the envelope of said first mentioned high frequencycurrent, means for impressing said first mentioned high frequencycurrent on one branch of said parallel circuit to vary the temperatureand thereby the resistance of the device connected therein at saidpredetermined frequency and for impressing said second mentioned highfrequency current on the other branch of said parallel circuit to varythe temperature and thereby the resistance of the device connectedtherein at said predetermined frequency whereby said unidirectionalelectromotive force alternately creates a pulsating current flow firstin one branch and then the other branch of said parallel circuit tocause the induction of an alternating electromotive force in thesecondary winding of said transformer of one phase or of opposite phasedepending upon the polarity of said unidirectional electromotive force,alternating current supply means for energizing both of saidoscillators, and inductive control means jointly energized by currentsdirectly supplied by said supply means and by alternating currentderived from the secondary winding of said transformer.

6. The combination with a small unidirectional source of electromotiveforce, a resistive device having an appreciable temperature coeflicientof resistance, and a transformer having its primary winding connected incircuit with said device and said source, of means continuously passingmodulated, high frequency current through said device to regularly varythe temperature of said device and thereby to regularly vary theresistance of said device.

7. The combination with a small unidirectional source of electromotiveforce, a resistive device having an appreciable temperature coeflicientof resistance, and a transformer having its primary winding connected incircuit with said device and said source, of means continuously passingmodulated high frequency current through said device to regularly varythe temperature of said device and thereby to regularly vary theresistance of said device, and amplifying means connected to thesecondary winding of the transformer.

8. The combination with a circuit including a resistive device having anappreciable temperature coefiicient of resistance, of means forimpressing a small unidirectional electromotive force on said circuit,means for continuously passing modulated high frequency current throughsaid resistance to regularly vary the temperature of said device andthereby to regularly vary the resistance of said device whereby saidforce creates a pulsating current flow in said circuit, and amplifyingmeans energized by said pulsating current flow.

9. In measuring apparatus, a source of direct current whose magnitude isto be measured, an electrical resistive device having an appreciabletemperature coefflcient of resistance through whichsaid direct currentis passed, a source of modulated high frequency current arranged toenergize said device independently of said direct current source, meansfor amplifying said first mentioned current after its passage throughsaid device, and means actuated by said amplified current for indicatingthe magnitude of said direct current.

10. The combination with a circuit including an electrical resistivedevice having an appreciable temperature coeflicient of resistance, ofmeans for impressing a small unidirectional electromotive force on saidcircuit, a modulated high frequency current source, and means forimpressing modulated high frequency curent from said source on saiddevice to vary the temperature of said device at the frequency of themodulations of said source. I

11.1'I'he combination of a thermocouple, an electrical resistive devicehaving an appreciable temperature coefiicient of resistance and atransformer having its primary winding connected in circuit for the flowof current from said thermocouple through said resistive device andprimary winding, a modulated high frequency current supply'source, andmeans for impressing high frequency current from said source on saidresistive device independently of said thermocouple to vary theresistance of said resistive device at the frequency of the modulationsof said source.

12. The combination of a thermocouple, an electrical resistive devicehaving an appreciable temperature coefficient of resistance and atransformer having a primary winding connected in circuit for the flowof current from said thermocouple through said resistive device andprimary winding, a modulated alternating current supply source, andmeans for impressing alternating current from said source on saidresistive device to vary the resistance of said resistive device at thefrequency of the modulations of said source.

13. The combination with a circuit including an electrical resistivedevice having an appreciable temperature coefllcient of resistance, ofmeans for impressing a small unidirectional electromotive force on saidcircuit, a modulated alternating current source, and means forimpressing modulated alternating current from said source on said deviceto vary the temperature of said device at the frequency of themodulations of said source.

HARRY S. JONES.

